The invention relates to a dial gauge comprising an illumination source below a dial plate, and a light guide arranged to guide illumination light from below the dial plate to the front side of the dial plate. In particular, although not exclusively, the invention relates to a mechanical pressure gauge including such a dial gauge.
Firefighters and other rescue personnel are often required to enter hazardous environments, such as burning buildings. In such circumstances, each firefighter is provided with a self-contained breathing apparatus (SCBA) which provides breathable gas to the firefighter. The breathing apparatus is typically provided with a mechanical pressure gauge for monitoring the remaining supply of breathable gas.
The mechanical pressure gauge is typically provided with an illumination source to illuminate the face of the dial plate so that the firefighter can read the gauge in low-light conditions. For example, it is known to provide a backlight behind a transparent or semi-transparent dial plate. It is also known to provide an illumination source around the periphery of a dial plate to illuminate the dial plate from its front side. Front side illumination sources may be used for opaque dial plates and for photoluminescent dial plates, which re-emit light after deactivation of illumination. Whilst dial gauges having such illumination arrangements may be satisfactory, they may require a plurality of illumination sources in order to provide relatively uniform illumination over the dial plate, which results in a relatively high power consumption. Further, in the case of photoluminescent dial plates, any non-uniform illumination of the dial face may lead to brighter glowing photoluminescent hot spots, which may make the dial gauge more difficult to read.
It is therefore desirable to provide an improved dial gauge having an improved arrangement for illuminating the dial plate.